The invention relates to a method for operating an internalcombustion engine especially of a motor vehicle wherein the fuel, which is to be injected for a combustion, is injected directly into the combustion chamber of a cylinder in a first operating mode during an induction phase and in a second operating mode during a compression phase and is thereafter ignited in both operating modes. In this method, nitrogen oxides, which develop during the combustion, are stored in a catalytic converter. Likewise, the invention relates to an internal combustion engine especially for a motor vehicle having an injection valve with which the fuel, which is to be injected for a combustion, can be injected directly into a combustion chamber of a cylinder in a first operating mode during an induction phase and in a second operating mode during a compression phase. The engine includes a spark plug with which the injected fuel can be ignited in both operating modes and also includes a catalytic converter for storing nitrous oxides developing during the combustion. The engine has a control apparatus for controlling (open-loop and/or closed-loop) operating variables of the engine in both operating modes.
Systems for the direct injection of fuel into the combustion chamber of an internal combustion engine are generally known. In these systems, a first operating mode, a so-called homogeneous operation, and a second operating mode, a so-called stratified charge operation or, in short, stratified operation are distinguished. The stratified operation is used especially for small and medium loads; whereas, the homogeneous operation is used when larger loads are applied to the engine.
In the stratified operation, the fuel is injected into the combustion chamber during the compression phase of the engine in such a manner that a fuel cloud is disposed at the time point of the ignition in the direct vicinity of a spark plug. This injection can take place in different ways. Accordingly, it is possible that the injected fuel cloud is already during or directly after the injection in the vicinity of the spark plug and is ignited thereby. Likewise, it is possible that the injected fuel cloud is guided by a charge movement to the spark plug and is only then ignited. In both combustion methods, no uniform fuel distribution is present; instead, a stratified charge is present.
The advantage of the stratified operation is that the applied small and medium loads can be carried out by the engine with a very small amount of fuel. However, larger loads cannot be satisfied by the stratified operation.
In the homogeneous operation which is provided for such larger loads, the fuel is injected during the induction phase of the engine so that a swirling and therefore a distribution of the fuel in the combustion chamber can easily take place. To this extent, the homogeneous operation corresponds approximately to the mode of operation of internal combustion engines wherein the fuel is injected into the intake manifold in the conventional way. As required, the homogeneous operation can be used also for smaller and medium loads.
In stratified operation, the throttle flap is opened wide in the intake manifold leading to the combustion chamber and the combustion is essentially controlled (open-loop and/or closed-loop) only by the fuel mass to be injected. In the homogeneous operation, the throttle flap is opened or closed in dependence upon the requested torque and the fuel mass, which is to be injected is controlled (open-loop and/or closed-loop) in dependence upon the inducted air mass.
In both modes of operation (that is, in stratified operation and in homogeneous operation), the operating variables for the injection of fuel (that is, the injection duration and the injection start, for example) and the operating variables for the ignition of the injected fuel (that is, for example, the ignition time point) are controlled (open-loop and/or closed-loop) in dependence upon a plurality of additional operating variables of the engine to an optimal value with a view to saving fuel, reducing exhaust gas and the like. The control (open-loop and/or closed-loop) is different in the two operating modes.
It is perforce required that there be a switching back and forth between the two operating modes of the engine, that is, the homogeneous operation and the stratified operation. Here, it is required that these switchovers take place free of jolts.
The occurring exhaust gases are treated catalytically to reduce the emission of toxic substances. For this purpose, usually a three-way catalytic converter is provided with which HC compounds and CO compounds are oxidized and NOx compounds can be reduced. The last-mentioned nitrous oxides develop especially during the stratified operation. However, in this operating state, an oxygen excess is present because of the lean air/fuel mixture so that the nitrous oxides cannot be fully reduced in the three-way catalytic converter.
For this reason, an additional storage catalytic converter is assigned to the three-way catalytic converter wherein the nitrous oxides can be intermediately stored. The storage catalytic converter must again be discharged or emptied because of the limited storage capacity thereof. This takes place during the homogeneous operation of the engine. An oxygen deficiency is present during the homogeneous operation because of the rich air/fuel mixture. This has the consequence that the stored nitrous oxides are released from the storage catalytic converter and can be reduced by the three-way catalytic converter.
For this reason, it is necessary for a low toxic substance stratified operation of the engine that the storage catalytic converter is not completely charged and/or is discharged in time and therefore is not overloaded.
It is a task of the invention to provide a method for operating an internal combustion engine as well as an internal combustion engine wherein a required discharge of the storage catalytic converter can be carried out more conveniently.
This task is solved in a method of the above-mentioned kind in that a gear change into another gear stage and/or into another transmission ratio range and a switchover into the first operating mode are executed approximately simultaneously. The switchover into the first operating mode is provided for discharging the nitrous oxides stored in the catalytic converter. In an internal combustion engine of the type mentioned initially herein, the task is solved in accordance with the invention in that a gear change into another gear stage and a switchover into the first operating mode can be carried out by the control apparatus approximately simultaneously. The switchover into the first operating mode is provided for discharging the nitrous oxides which are stored in the catalytic converter.
With a gear change, a switchover of the operating mode into the homogeneous operation is executed approximately simultaneously. This has two advantages. On the one hand, it is achieved via the homogeneous operation that the storage catalytic converter is discharged. At the same time, an overcharge of the storage catalytic converter is thereby avoided. An output of nitrous oxides to the environment thereby does not take place. On the other hand, with the gear change, a possible jolt of the engine is covered over because of the operating mode change. The perception of such a jolt is therefore substantially minimized by the gear change. The engine thereby exhibits a quiet and uniform running even for a change of the operating mode.
In an advantageous embodiment of the invention wherein the gear change is required but wherein really no switchover into the first operating mode is necessary for the gear change, however the catalytic converter is filled, a switchover into the first mode of operation takes place approximately simultaneously with the gear change in order to discharge the catalytic converter. In this case, a gear change is required; a change of operating mode is, however, not really required. For discharging the storage catalytic converter, a switchover into the homogeneous operation, however, takes place during the gear change. In this way, an overcharge of the storage catalytic converter is, on the one hand, avoided. On the other hand, a jolt-free operating mode change is achieved.
In another advantageous embodiment of the invention, wherein the gear change is required, a switchover into the first operating mode takes place approximately simultaneously with the gear change in order to discharge the catalytic converter even though no switchover into the first mode of operation is really required for the gear change and the catalytic converter is not yet charged or only charged a small amount. This defines a precautionary discharge of the storage catalytic converter. Even though the storage catalytic converter is really not or only slightly charged, the converter is discharged early or in anticipation. In this way, an overcharge of the catalytic converter is reliably avoided.
In a further advantageous embodiment of the invention, wherein the catalytic converter is filled and wherein there is a switchover into the first operating mode in order to discharge the catalytic converter and wherein the gear change is really not required, the gear change is executed nonetheless simultaneously with the switchover into the first operating mode. This presents the reverse case. The gear change is not required but possible and purposeful. The discharge of the storage catalytic converter is, in contrast, necessary. In order that a possibly occurring jolt for the operating-mode change (which is to be executed) is perceptible as little as possible, a gear change is executed approximately simultaneously with the switchover into the homogeneous operation.
It is especially advantageous when the gear change into another gear stage is substituted with a switchoff of one of several cylinders. The methods and functions described above are therefore no longer executed in connection with a gear change into another gear stage; instead, and in lieu thereof, at least one of the cylinders of the engine is shut off. A cylinder switchoff of this kind has the consequence that the other cylinders must provide more power. For this purpose, it is necessary to control (open-loop and/or closed-loop) the other cylinders in a different manner. This transition to the higher power is then used in accordance with the invention to switch from the stratified operation into the homogeneous operation. In this way, it is achieved, on the one hand, that the storage catalytic converter is discharged by the homogeneous operation. On the other hand, with the cylinder switchoff, it is achieved that a possibly occurring jolt can hardly be perceived by the driver of the vehicle. This jolt occurs with the switchover of the operating mode.
Of special significance is the realization of the method of the invention in the form of a control element which is provided for a control apparatus of an internal combustion engine, especially of a motor vehicle. A program is stored on the control element which can run on a computing apparatus, especially on a microprocessor, and is suitable for executing the method of the invention. In this case, the invention is realized by a program stored on the control element so that this control element, which is provided with the program, defines the invention in the same manner as the method for which the program is suitable for carrying out. An electrical storage medium can be utilized as a storage element such as a read-only-memory.